Electrodeposition of aluminium

ABSTRACT

THE PRESENT INVENTION RELATES TO THE IMPROVEMENTS OF THE ELECTRODEPOSITION OF ALUMINIUM AND CHARACTERISED BY USING A BATH COMPRISING, AS A SOLVENT, AT LEAST ONE MEMBER FROM THE GROUP CONSISTING OF TETRAHYDROFURAN AND ITS DERIVATIVES AND, AS SOLUTES, (A) AN ALUMINUM HALIDE AND (B) AT LEAST ONE OF LITHIUM ALUMINIUM HYDRIDE AND LITHIUM HYDRIDE, IN WHICH THE MOLAR RATIO OF THE SOLUTES IS 1 TO 3. ONE OR MORE AROMATIC COMPOUNDS SUCH AS BENZENE TOGETHER WITH A CHAIN ETHER MAY BE ADDED TO SAID BATH. ACCORDING TO THE PRESENT INVENTION, SMOOTH, HIGH DENSITY, DUCTILE AND COHERENT ALUMINIUM FILM CAN BE DEPOSITED ON THE CATHODE BODY.

United States Patent Olfice Patente July 27, l97ll US. Cl. 204-14 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to the improvements of the electrodeposition of aluminium and characterised by using a bath comprising, as a solvent, at least one member from the group consisting of tetrahydrofuran and its derivatives and, as solutes, (a) an aluminium halide and (b) at least one of lithium aluminium hydride and lithium hydride, in which the molar ratio of the solutes is l to 3. One or more aromatic compounds such as benzene together with a chain ether may be added to said bath. According to the present invention, smooth, high density, ductile and coherent aluminium film can be deposited on the cathode body.

The present invention belongs to the field of art of an electrochemistry, particularly to metal deposition by an electrochemical process including a plating and a refining of aluminium metal.

It has been already known in the electrolytic deposition of an aluminium that such bath may be used as consisting of aluminium chloride, lithium aluminium hydride and/or lithium hydride as a solute While a tetrahydrofuran as a solvent. However, any fact showing the successful result has not been reported in the use of the tetrahydrofuran as the solvent. In Journal of the Electrochemical Society of June 1952, it is disclosed that a desired result was not obtained by the use of the tetrahydrofuran as the solvent. The process of electroplating using a bath consisting of aluminium chloride, ether and lithium hydride of lithium aluminium hydride has been presented by Abner Brenner and Dwight E. Couch to which US. Pat. No. 2,651,608 was given on Sept. 8, 1953. In this patented specification, the tetrahydrofuran and/or its derivatives are not disclosed.

The present invention relates to an electrodeposition of an aluminium, particularly to a method of depositing the aluminium on a cathode electrode in the use of the tetrahydrofuran and/or the derivatives thereof as the solvent for the solute.

An object of the present invention is to provide a method of depositing an aluminium having a high density, non-porosity, ductile and very coherent.

Another object of the present invention is to provide an improved method of plating electrochemically the aluminium layer or film on metallic articles other than aluminium, said layer or film having very smooth surfaces, a high density, high purity and good ductility.

A further object of the present invention is to pro vide a method of refining electrochemically aluminium materials, thereby very pure aluminium materials are obtained elfectively.

According to the present invention, in order to perform the above objects, the following bath composition is prepared in which the solvent comprises at least one member of the group consisting of tetrahydrofurans and derivatives thereof and, as solutes, (a) an aluminium halide and (b) at least one of lithium hydride and lithium aluminium hydride in which bath the concentration of component (a) is 0.7 mol per liter, and the molar ratio of the solutes is 1 to 3, as calculated by the following equation;

n=the mole ratio of the solutes.

X=the total number of moles of the aluminium halide in the bath.

Y=the total number of moles of the lithium aluminium hydride in the bath.

Z=the total number of moles of the lithium hydride in the bath.

The aluminium halide to be added to the bath may be an aluminium chloride, an aluminium bromide or an aluminium iodide and two or three kinds of these aluminium halides may be added together. The derivatives of tetrahydrofuran preferable to carry out the process according to the present invention are 2,3-dichlorotetrahydrofuran, Z-methyl 3 chlorotetrahydrofuran, 3-bromotetrahydrofuran, Z-methyltetrahydrofuran and Z-dimethyltetrahydrofuran.

In the aluminium electrodeposition process, it has been known that various ethers are desirable as the solvent. An attempt was made to use the tetrahydrofuran as the solvent for an aluminium halide or a lithium aluminium hydride, but such attempt ended in failure. That is, ductile and smooth films of aluminium having a high density could not be obtained.

. It is known that the aluminium films or layers deposited on the cathodic articles by using a hydride bath are fair, ductile and coherent, when the bath comprises chain ethers as the solvent. However, the hydride bath comprising the lithium hydride and/or lithium aluminium hydride has some disadvantages as described hereunder.

The aluminium from the aluminium chloride in the bath deposits onto a cathode in accordance with the proceeding of the electrolytic operation and an aluminium dissolves into the bath from an anode composed of an aluminium material having a high purity. This aluminium dissolved into the bath from the anode makes a compound different from the aluminium compounds existing in the bath originally. Therefore, the dissolved aluminium from the anode is non-elfective for the plating. During the electrolytic operation a hydrogen gas generates from a part of bath adjacent the anode, so that the hydride compounds are consumed by this generated hydrogen gas to accelerate the aging of the bath. In order to continue effectively the electrolysis operation the additional lithium aluminium hydride and/ or lithium hydride should be added to the bath to compensate the consumed aluminium.

Therefore, the aluminium plating using the hydride bath is very expensive, so that the applications are limited to particular objects.

The present invention provides a process having not the aforesaid disadvantages in the electrodeposition of aluminium using the hydride bath in the prior art. The bath according to the present invention comprises at least one of the tetrahydrofuran and its derivatives as the solvent for the aluminium halides, the lithium alu minium hydride and the lithium hydride, each being a solute and the molar ratio n of the solutes is restricted to 1 to 3.

In the present invention, the molar ratio 11 of the solutes is selected to be 1 to 3. The films or layers of aluminum plated on the cathodic articles are white, ductile, smooth and coherent. The bath could be used for a long time. If the anode of aluminium of high purity continuously supply to compensate its consumption due to the electrolysis operation, the bath can be effective for a very long time. The reason is that an aluminium of amount equivalent to the consumed amount of aluminium in the bath dissolves into the bath from the anode. This continuous operation is possible in only the range of 1 to 3 of the molar ratio of the solutes.

If the molar ratio is less than 1, the aluminium film or layer plated on the cathode body will be gray and anode was 32.6 g. It is clear from these results that the deposited amount of aluminium is substantially equal to the dissolved amount from the anode in the process according to the present invention so that the composition of the bath is maintained substantially unchanged. Therenot coherent, so that good deposited film or layer can 5 fore, a continuous electrolysis carried out through a long not be obtained. Further, in case the molar ratio is less period is possible under the condition that the bath is inthan 1, the time necessary for the deposition producing sulated from the atmosphere by an inert gas such as argon. the desired film and layer will be extended than the case The current efiiciency in the case A is 97.6% at the cathof the deposition being carried out in said range. If the ode and 103% at the anode and in the experiment B is molar ratio is more than 3, the dissolution of aluminium 99.4% at the cathode and 103% at the anode. As clear into the bath from the anode will be impossible. Some from Table 1, the current efficiency at the anode is more complex compound generates in the bath solution at only than 100%. According to the bath in the present inventhe range between 1 and 3 of the molar ratio. This comtion, even if the aluminium consisting an anode is an plex compound does not exist in the bath when the bath aluminium material of relatively low purity, the aluminsolution does not have the molar ratio out of said range. ium with very high purity such as 99.99% will be deposited In the present invention, an amount of aluminium subonto a cathode. This makes possible the refining of low stantially equivalent to the amount of aluminium deposited purity aluminium to high purity aluminium such as onto the cathode dissolves into the bath solution from the 99.996% aluminium. anode composed of an aluminium by the complex com- In the present invention, in order to increase the pound in the bath. Therefore, the aluminium existing in aluminium concentration in the bath, one or more of the bath is consumed without any additional supply of aromatic compounds having the benzene ring structure aluminium from the anode, so that the electrolysis beare added to the bath comprising aluminium halide, comes impossible after a short time from beginning of lithium hydride and/or lithium aluminium hydride and the electrolysis. tetrahydrofuran and/ or its derivatives. The aromatic com- While the molar ratio n of the solutes was explained pounds may be benzene, toluene, xylene, chlorobenzene, as the essential point of the present invention, also the dichlorobenzene and chlorotoluene. These aromatic hyaluminium concentration in the bath is an important drocarbons and aromatic halides may be used selectively. matter to the deposition. In the present invention, the The saturated concentrated of aluminium, particularly aluminium concentration of the bath is kept to at least aluminium chloride, in the bath can be increased by add- 0.7 mole per litre of the solvent. If the aluminium coning one or more of the aforementioned aromatic comcentration is less than 0.7 mole per litre of the solvent, pounds as a solvent to the bath. In the bath comprising the aluminium films or layers deposited onto the cathodic the aromatic compound, the saturated concentration of article will become undesirable and the time of electroaluminium reaches 3.0 moles per a litre of the solvent. lytic operation must be extended to obtain a desired In the practical experiment according to the present inthickness thereof. Therefore, it is not economical to reduce vention, when only tetrahydrofuran was used as a solvent, the aluminium concentration of the bath to the value the maximum concentration of aluminium to the solvent less than 0.7 mole/l. The upper limit of the aluminium was 2.5 moles per litre of said solvent at a temperature of concentration depends upon the composition of bath, 25 C., while when by volume of benzene was particularly the kind of the solvent. The upper limit of 49 added thereto, the maximum concentration of aluminium the aluminium concentration corresponds to the satuwas increased up to 3.0 moles per litre of the solvent comrated concentration of aluminium in the solvent. For posed of the tetrahydrofuran and the benzene at the same example, in case the solvent is tetrahydrofuran, said limit temperature. When only 10% by volume of benzene is is 2.5 moles per litre of said solvent. added to the solvent (tetrahydrofuran), the maximum The condition of electrolysis can be selected suitably, concentration of aluminium reaches 2.6 moles per litre however, it is preferable that the current density is 0.5 of tetrahydrofuran. Regarding the amount of the benzene to 10.0 a./dm. and the temperatures of the bath is 18 to be added to the tetrahydrofuran, an amount between to 27 C. 10 to 40% by volume is preferable. If said amount is less As described above, according to the present invention than 10%, the effect of the benene is inconsequential. the aluminium electrodeposition can be carried out with- 50 Further, the composite bath comprising tetrahydroout any of the disadvantages which have not been avoided furan and benzene in the desired proportions has a specific by the prior art. The present invention has the undermenconductance larger than that of the bath of tetrahydrotioned effects and advantages. furan only. That is, the specific conductance of the bath in- The amount of aluminium substantially equivalent to cluding tetrahydrofuran as a solvent, of which the molar the amount of aluminium dissolved into the bath from ratio of the solutes n is 1, shows 1.5 10 t2 cm.- at an anode deposits to a cathode. This matter may be proved 20 C., while the specific conductance of the composite by the facts as shown by Table 1. bath consisting of by volume tetrahydrofuran and TABLE 1 Electrolyte bath Cathode Tetra- Amount Amount hydro- Current of Current of Current 01 (A1013! Al fnran density Voltage deposited eflicieney dissolved efiicieney LlAl H4) (mol/l.) (ml.) (a./dm. (v.) Al (g.) (percent) A1(g.) (percent) As seen from Table 1, in both experiments A and B, 30% by volume of benzene, of which the molar ratio of the bath consisting of aluminum chloride, lithium aluminthe solutes n is 1, shows 4 10 -Q cm.- at the same ium hydride and tetrahydrofuran was used. The molar 7O temperature. Therefore, the bath comprising the benzene ratio of the solutes is 2.0 in A while it is 1.5 in B. In A, the amount of aluminium deposited onto the cathode was 28.5 g. and the amount of aluminium dissolved into the bath from the anode was 29.7 g. In B, the amount of aluminium deposited onto the cathode was 31.4 g. and

decrease the time necessary for the deposition of aluminium of the predetermined amount in comparison with the bath comprising tetrahydrofuran and/ or its derivative but not the benzene.

The saturated concentration of aluminium chloride in the amount of aluminium dissolved into the bath from the the bath comprising tetrahydrofuran and/ or its derivative is increased by adding benzene of the predetermined amount thereto, as aforesaid. The saturated concentration of aluminium chloride is further increased by adding additionally one or more chain ethers. The additive ether may be selected from among a group consisting of ethyl ether (diethyl ether), propyl ether (n-propyl ether), butyl ether (n-butyl ether), isopropyl ether, phenyl methyl ether (anisole), and ethyl phenyl ether (phenetole). When one or more of said ethers are added to the bath, the saturated concentration of aluminium will be 3.5 moles per a litre of the solvent including said ether or ethers.

In case the solvent is a mixture of tetrahydrofuran and one or more kinds of ether other than the tetrahydrofuran, it is preferable that the ratio of the amount of benzene to the mixture is within the range between and 50% by volume.

Examples of the present invention are as follows.

EXAMPLE. 1

Tetrahydrofuran of 100% was used as a solvent. The mixture of aluminium chloride of 0.5 mole per a litre of said solvent and lithium aluminium hydride of 0.35 mole per a litre of said solvent was used as a solute. An aluminium plate of 99.99% purity was used as an anode. The molar ratio of the solute n is about 1.43. The cathode was a usual copper plate. The electrolysis was carried out with the current density of 1 a./dm. and at the temperature of 20 C. The deposited aluminium film on the cathode was silver-white, ductile and coherent. In the same bath, an aluminium plate of 99.0% purity Was used as the anode and the electrolysis was carried out with the same conditions as the above for 11 hours. The thickness of aluminium film deposited on the cathode (copper plate) was 0.08 mm. and its purity was 99.99%.

EXAMPLE 2 Tetrahydrofuran of 100% was used as a solvent. The mixture of aluminium chloride of 0.4 mole per a litre of said solvent, aluminium bromide of 0.15 mole per a litre of said solvent and lithium aluminium hydride of 0.3 mole per a litre of said solvent was used as a solute. The molar ratio n of the solute is about 1.83. An aluminium plate having the purity of 99.99% was used as an anode. A steel plate was used as a cathode. The electrolysis was carried out at the temperature of 25 C. with the current density of 4 a./dm.

The aluminium film deposited on the cathode was silverwhite, ductile and very coherent.

In the place of said aluminium plate of the 99.99% purity, an aluminium plate of 99.0% purity was used as an anode. In this treatment, after the continuous electrolysis was carried out for 5 hours at the temperature of 25 C. with the current density of 4 a./dm. the aluminium film having the thickness of 0.06 mm. was obtained on the cathode and its purity was 99.996%.

EXAMPLE 3 Tetrahydrofuran of 100% was used as a solvent. Aluminium chloride of 1.2 moles per a litre of said solvent and lithium aluminium hydride of 0.35 mole per a litre of said solvent were used as a solute. The molar ratio n of solutes is about 2.26. An aluminium plate having the purity of 99.99% was used as an anode. A steel plate was used as a cathode. The electrolysis was carried out at the temperature of 25 C. with the current density of 4 amp/dmF.

The aluminium plating fil-m deposited on the cathode from the bath mentioned above was silver-white, ductile and very coherent.

Using this bath, when an aluminium plate having the purity of 99.0% was used in the place of the aluminium plate having the purity of 99.99%, an aluminium plating film having the thickness of 0.12 mm. and the purity of 99.996% after the continuous treatment for 5 hours at the temperature of 25 C. with the current density of 4 amp/dm. was obtained.

6 EXAMPLE 4 The mixture of 96% by volume of tetrahydrofuran and 4% by volume of 2,3-dichlorotetrahydrofuran was used as a solvent. Aluminium chloride and lithium aluminium hydride were used as a solute. The concentration of aluminium chloride to a litre of said mixture solvent was 1.1 moles and the concentration of lithium aluminium hydride to a litre of said mixture solvent was 0.5 mole. Therefore, the molar ratio n of the solutes is about 2.2. An aluminium plate having the purity of 99.99% was used as an anode. A steel plate was used as a cathode. The electrolysis was carried out at the temperature of 25 C. with the current density 4 a./dm.

An aluminium plating film deposited onto the steel plate was silver-white, ductile and very coherent.

An aluminium plate having the purity of 99.0% was used in the place of said aluminium plate of 99.99% in the same bath as above. The electrolysis was carried out at the temperature of 25 C. with the current density of 4 a./dm. for 5 hours. As the result of this treatment, the aluminium plating film deposited onto the cathode had the thickness of 0 .13 mm. and the purity of 99.99%.

EXAMPLE 5 The mixture of by volume of tetrahydrofnran and 5% by volume of Z-methyl, 3-chlorotetrahydrofuran was used as a solvent. As a solute, aluminium chloride of 0.9 mole per a litre of said solvent mixture and lithium aluminium hydride of 0.4 mole per a litre of said solvent mixture were used. Therefore, the molar ratio n of the solutes is about 2.25. An aluminium plate having the purity of 99.99% was used as an anode. A steel plate was used as a cathode. The electrolysis was carried out at the temperature of 25C. with the current density of 3 a./dm.

The aluminium plating film deposited onto the cathode was silver-white, ductile and very coherent.

The electrolysis was carried out in the use of the above bath under the same condition as the above mentioned condition continuously for 5 hours, wherein the aluminium plate having the purity of 99.0% was used as the anode in the place of the aluminium plate of 99.99% purity. As the result of this treatment, the aluminium film having the thickness of 0.08 mm. and the purity of 99.99% was deposited onto the cathode.

The bath comprising tetrahydrofuran as a solvent shows excellent characteristics for the electrodisposition of aluminium as described above. The characteristics of said bath are further improved by adding one or more aromatic compounds having a benzene ring structure such as benzene, toluene, xylene, chlorobenzene and chlorotoluene. An example of the use of said aromatic compound is as under.

EXAMPLE 6 The mixture of 56% by volume of tetrahydrofuran and 44% by volume of benzene Was used as a solvent. As a solute, aluminium chloride of 0.6 mole per a litre of said solvent mixture and lithium aluminium hydride of 0.6 mole per a litre of said solvent mixture were used. The molar ratio n of the solute is 1. An aluminium plate having the purity of 99.99% was used as an anode. A steel plate was used as a cathode. The electrolysis was carried out at the temperature of 20 C. with the current density of 3 amp/dm.

An aluminium film plated on the cathode of steel plate was silver-white, ductile and very coherent.

In the case of the use of an aluminium plate having the purity of 99.0% as the mode, an aluminium film having the thickness of 0.12 mm. and the purity of 99.99% was also deposited on the cathode after the treatment for 5 hours.

EXAMPLE 7 The mixture of 50% by volume of tetrahydrofuran, 10% by volume of n-butyl ether and 40% by volume of toluene is used as a solvent. As a solute, aluminium chloride of 0.71 mole per a litre of said solvent mixture, aluminium bromide of 0.09 mole per a litre of said solvent mixture and lithium aluminium hydride of 0.47 mole per a litre of said mixture were used. An aluminium plate having the purity of 99.99% was used as an anode. A steel plate was used as a cathode. The molar ratio n of the solutes is about 1.7. The electrolysis was carried out at the temperature of 25 C. with the current density of 2 amp/drn.

, The aluminium film deposited on the cathode was silverwhite, ductile and very coherent.

The aluminium plating film n the cathode in the use of the above mentioned bath and the aluminium plate having the purity of 99.0% as an anode had the thickness of 0.065 mm. after the continuous treatment for hours under the same condition as the above.

EXAMPLE 8 The mixture of 30% by volume of tetrahydrofuran, 40% by volume of dichlorobenzene and 30% by volume of propyl ether was used as a solvent. As a solute, aluminium chloride of 1.65 moles per litre of said mixture solvent and lithium hydride of 2.64 moles per litre of said mixture solvent. The molar ratio n of the solutes is 1.5. An aluminium plate having the purity of 99.99% was used as an anode. A steel plate was used as a cathode. The electrolysis was carried out at the temperature of 25 C. with the current density of 4 amp./dm.

An aluminum film deposited onto the cathode was silver-White, ductile and very coherent.

Even when an aluminium plate having the purity of 99.0% was used as an anode, an aluminium film having the thickness of 0.12 mm. and the purity of 99.99% was plated onto the cathode.

As aforesaid, according to the present invention a fine, smooth, ductile, silver-white and coherent aluminium coating film can be plated onto the cathode body, this aluminium film becomes glossy when the bath comprising polyvinyl chloride and/or 1,2-dichloroethane is used. This is one of characteristic features of the present invention. The amount of the additive for making the surface of deposited aluminium film glossy is preferably 1-3 g. per a litre of the used solvent. In each of the baths shown in Examples 1 to 3, 5, 6 and 8, when polymerization grade of polyvinyl chloride of 2 g./l. was used, very glossy film was obtained. This additive does not affect the characteristics of the plated film deposited from the baths according to the present invention.

What is claimed is:

1. A method for electrodepositing aluminum on a cathode body which comprises passing an electrolyzing current from an anode to said cathode body through a non-aqueous bath comprising at least one member of the group consisting of tetrahydrofuran, 2,3-dichlorotetrahydrofuran, 2- methyl-3-chlorotetrahydrofuran, 3-bromotetrahydrofuran, Z-methyltetrahydrofuran and 2-dimethyltetrahydrofuran as a solvent, an aluminum halide, and at least one of lithium hydride and lithium aluminum hydride as solutes, wherein the aluminum concentration in the bath is at least 0.7 mol per liter of the solvent, the molar ratio of the solutes is 1 to 3 as given by the following equation:

where n is the molar ratio of solutes,

X is the total number of mols of aluminum halide,

Y is the total number of mols of lithium aluminum hydride,

Z is the total number of mols of lithium hydride.

2. A method for electrodepositing aluminum on a cathode body according to claim 1 wherein said bath further comprises 10 to 40% by volume of at least one member of the group consisting of benzene, toluene, xylene, chlorobenzene, dichlorobenzene, and chlorotoluene.

3. A method for electrodepositing aluminum on a cathode body according to claim 2 wherein said bath further comprises at least one chain ether from the group consisting of ethyl-ether, propyl-ether, butyl-ether, isopropylether, phenyl-methyl-ether and ethyl-phenyl-ether, with the ratio of the amount of said aromatic compound to the mixtures of said chain ethers and said tetrahydrofuran or derivative thereof being 5 to 50% by volume.

4. A method for electrodepositing aluminum on a cathode body according to claim 1 wherein at least one substance selected from the group consisting of polyvinyl chloride and 1,2-dichloroethane is added to the bath in an amount of 1 to 3 grams per liter of solvent to render the deposited aluminum glossy.

5. A method for electrodepositing aluminum on a cathode body according to claim 2 wherein at least one substance selected from the group consisting of polyvinyl chloride and 1,2-dichloroethane is added to the said bath in an amount of 1 to 3 grams per liter.

6. A method for electrodepositing aluminum on a cathode body according to claim 3 wherein at least one substance selected from the group consisting of polyvinyl chloride and 1,2-dichloroethane is added to the bath in an amount of 1 to 3 grams per liter.

7. A method for electrodepositing aluminum on a cathode body according to claim 1 wherein the solvent consists essentially of tetrahydrofuran and 2,3-dichlorohydrofuran and the solute is aluminum chloride, 1.1 mols per liter, and lithium aluminum hydride, 0.5 mol per liter.

8. A method for electrodepositing aluminum on a cathode body according to claim 2 wherein the solvent consists essentially of 56% by volume tetrahydrofuran and 44% by volume of benzene, and the solute is aluminum chloride, 0.6 mol per liter, and lithium aluminum hydride, 0.6 mol per liter.

9. A process for electrodepositing aluminum on a cathode body according to claim 3 wherein the solvent consists essentially of 50% by volume tetrahydrofuran, 40% by volume toluene and 10% by volume n-butylether and the solute is aluminum chloride 0.71 mole per liter, aluminum bromide 0.09 mol per liter, and lithium aluminum hydride 0.47 mol per liter.

10. A process for electrodepositing aluminum on a cathode body according to claim 8 wherein polyvinyl chloride is added to the bath in an amount of 1 to 3 grams per liter.

References Cited UNITED STATES PATENTS 9/1953 Brenner 204-141 8/1966 McGraw 204-14.1

OTHER REFERENCES PATRICK P. GARVIN, Primary Examiner 

3. ONE OR MORE AROMATIC COMPOUNDS SUCH AS BENZENE TOGETHER WITH A CHAIN ETHER MAY BE ADDED TO SAID BATH. ACCORDING TO THE PRESENT INVENTION, SMOOTH, HIGH DENSITY, DUCTILE AND COHERENT ALUMINIUM FILM CAN BE DEPOSITED ON THE CATHODE BODY. 